The Role of Hydration Status in Diver Performance

This study will evaluate the effects of rehydration strategy on
terrestrial performance and overnight recovery following
immersion induced dehydration.

Principal Investigator: David Hostler

Funding Agency: Navy Sea Systems

Period: 06/15 - 06/18

Abstract: This study will evaluate the effects of
rehydration strategy on terrestrial performance and overnight
recovery following immersion induced dehydration. Previous
experimental approaches have assumed that water immersion led
to dehydration by an immersion-induced diuresis that was
thought to negatively affect exercise performance both in
water and after regress. Data from our lab and others suggests
that the immersion-induced diuresis does reduce the plasma
volume when autotransfusion forces water from the
intracellular and interstitial spaces into the intravascular
space but does not lead to a true dehydration and
will not compromise the diver while in water. While immersed,
a new homeostatic set point is reached and the diver
is effectively euhydrated as long as he remains in the
water. Prehydration or rehydrating while immersed
in water before this new set point is achieved would result in
a plasma volume expansion that would cause further diuresis.
After regressing from the water, however, there is a rapid
and significant drop in plasma volume as the water leaves
the vascular compartment and returns to the interstitial
space and cells resulting in hypohydration. This drop in
plasma volume after returning to land could
compromise venous return and thus cardiac output,
especially during exercise.

While hypohydration beyond a certain level impairs
performance, overhydration is also undesirable. The doctrine
of “drinking to stay ahead of thirst” has
been associated with exercise-associated hyponatremia,
which has occasionally proven fatal in soldiers and,
in divers, carries the additional risk of pulmonary edema. The
potential for pulmonary edema is complicated by the
translocation of fluid to the thorax resulting in increased
fluid and reduced volumes in the lung. Athletes and workers
tend to voluntarily drink less fluid than is lost from sweating.
Overhydration is almost always the result of bad
training recommendations or misunderstanding fluid homeostasis
by the individual. Body mass can be used to gauge sweat losses
and fluid requirements in the short term but multiple studies
have reported that soldiers operating in both cool and hot
environments can drink according to individual desire (ad
libitum) without experiencing excessive hypohydration or
poor performance. Hydrating during immersion is analogous to
attempting to hyperhydrate on land.

In aggregate, the previous studies performed for land-based
activities demonstrate both knowing both when and how much to
drink during activity is important. With regards to
rehydration, the scenario of a diver transitioning from
water-based to terrestrial activity requires
careful examination. Increased water loss from both
cold and warm environments adds additional complexity and
should be examined before recommendations for rehydration can
be made.